1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having regularly spaced driving teeth thereon, that is particularly adaptable to be used in an environment requiring that the belt remain flexible at low temperatures with the system under a small load.
2. Background Art
Toothed power transmission belts are used in a number of different environments. As examples, it is common to use a toothed belt for a printer carriage belt, a bill transportation belt, a card transportation belt, etc.
It is known to make the load carrying cords in this type of belt from aramid fibers. Aramid fibers have high strength and a high modulus which gives excellent dimensional stability in a heated environment as compared to cords made from other types of organic fibers.
In Japanese Patent Laid-Open 135954/1979, an aramid fiber load carrying cord is shown with a twist coefficient of 1.4-2.6 and a diameter of 300-500 denier.
It is also known to construct a load carrying cord by bundling and twisting a plurality of raw aramid fibers and applying an adhesive treatment thereto. This increases the cord's resistance to flexing fatigue and reduces the tendency of the cord to fray.
While a toothed belt using load carrying cords made from aramid fiber, as discussed above, is desirable for the reasons stated, these belts may lack the requisite flexibility in environments in which there is a small shaft load, as on small motors used with a printer carriage belt, a bill transportation belt, a card transportation belt, or the like. At low temperatures, this type of belt typically becomes highly rigid, which may require a high starting torque and cause exertion of a large load on pulley shafts about which the belt is trained. The result of exerting this large load on the shaft may be excessive heat generation, abnormal sound development, and/or localized abrasion in the contact areas of the belt. To overcome these problems, shortcomings, the entire system, including the belt, may have to be made larger than desirable. Further, due to the high required starting torque, the capacity of the motor may have to be increased over that which is desired, which adds to the cost of manufacture and operation of the overall system.